815 research outputs found
The H Beta Index as an Age Indicator of Old Stellar Systems: The Effects of Horizontal-Branch Stars
The strength of the H index has been computed for the integrated
spectra of model globular clusters from the evolutionary population synthesis.
These models take into account, for the first time, the detailed systematic
variation of horizontal-branch (HB) morphology with age and metallicity. Our
models show that the H index is significantly affected by the presence
of blue HB stars. Because of the contribution from blue HB stars, the H
does not monotonically decrease as metallicity increases at a given age.
Instead, it reaches a maximum strength when the distribution of HB stars is
centered around 9500 K, the temperature where the H index becomes
strongest. Our models indicate that the strength of the H index
increases as much as 0.75 {\AA} due to the presence of blue HB stars.
The comparison of the recent Keck observations of the globular cluster system
in the Milky Way Galaxy with those in giant elliptical galaxies, NGC 1399 and
M87, shows a systematic shift in the H against metallicity plane. Our
models suggest that this systematic difference is understood if the globular
cluster systems in giant elliptical galaxies are several billion years older,
in the mean, than the Galactic counterpart. Further observations of globular
cluster systems in the external galaxies from the large ground-based telescopes
and space UV facilities will enable to clarify whether this difference is
indeed due to the age difference or other explanations are also possible.Comment: 21 pages, 8 figures, Accepted for publication in the Astronomical
Journal, August 2000 issue, Postscript files are available at
http://csaweb.yonsei.ac.kr/~hclee/Hbet
In utero exposure to Î9âtetrahydrocannabinol leads to postnatal catchâup growth and dysmetabolism in the adult rat liver
The rates of gestational cannabis use have increased despite limited evidence for its safety in fetal life. Recent animal studies demonstrate that prenatal exposure to Î9âtetrahydrocannabinol (Î9âTHC, the psychoactive component of cannabis) promotes intrauterine growth restriction (IUGR), culminating in postnatal metabolic deficits. Given IUGR is associated with impaired hepatic function, we hypothesized that Î9âTHC offspring would exhibit hepatic dyslipidemia. Pregnant Wistar rat dams received daily injections of vehicular control or 3 mg/kg Î9âTHC i.p. from embry-onic day (E) 6.5 through E22. Exposure to Î9âTHC decreased the liver to body weight ratio at birth, followed by catchâup growth by three weeks of age. At six months, Î9âTHCâexposed male offspring exhibited increased visceral adiposity and higher hepatic triglycerides. This was instigated by augmented expression of enzymes involved in triglyceride synthesis (ACCα, SCD, FABP1, and DGAT2) at three weeks. Furthermore, the expression of hepatic DGAT1/DGAT2 was sustained at six months, concomitant with mitochondrial dysfunction (i.e., elevated p66shc) and oxidative stress. Interest-ingly, decreases in miRâ203aâ3p and miRâ29a/b/c, both implicated in dyslipidemia, were also observed in these Î9âTHCâexposed offspring. Collectively, these findings indicate that prenatal Î9â THC exposure results in longâterm dyslipidemia associated with enhanced hepatic lipogenesis. This is attributed by mitochondrial dysfunction and epigenetic mechanisms
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Implementation of a new urban energy budget scheme in the MetUM. Part I: Description and idealized simulations
This paper describes the formulation of a new urban scheme, MORUSES (Met OfficeâReading Urban Surface Exchange Scheme) for use in the Met Office Unified Model. The implementation of the new scheme ensures that (1) the new scheme offers more flexibility in the parametrization of the building properties, and hence provides a more realistic representation of the fluxes; (2) the bulk outputs are in satisfactory agreement with previous observational studies; and (3) the impact of the new scheme on the energy balance fluxes is similar to the impact of the current urban scheme when set up to mimic it. As well as having a better physical basis, MORUSES also gains in flexibility in applications and adaptations to different urban materials as well as urban planning. The new scheme represents the urban area as a composition of two tiles, a canyon and a roof, using a simple 2D geometry. Sensitivity analysis to canyon geometry and thickness of the roof canopy emphasizes the gain in flexibility captured by the new scheme. Copyright © 2010 Royal Meteorological Society and Crown Copyrigh
Survey of H-alpha emission from thirty nearby dwarf galaxies
Measurements of the H-alpha flux from 30 neighboring dwarf galaxies are
presented. After correction for absorption, these fluxes are used to estimate
the star formation rate (SFR). The SFR for 18 of the galaxies according to the
H-alpha emission are compared with estimates of the SFR from FUV magnitudes
obtained with the GALEX telescope. These are in good agreement over the range
log[SFR] = [-3,0]M sun/yr.Comment: 18 pages, 10 figures, 3 table
The North Ecliptic Pole Wide survey of AKARI: a near- and mid-infrared source catalog
We present a photometric catalog of infrared (IR) sources based on the North
Ecliptic PoleWide field (NEP-Wide) survey of AKARI, which is an infrared space
telescope launched by Japan. The NEP-Wide survey covered 5.4 deg2 area, a
nearly circular shape centered on the North Ecliptic Pole, using nine
photometric filter-bands from 2 - 25 {\mu}m of the Infrared Camera (IRC).
Extensive efforts were made to reduce possible false objects due to cosmic ray
hits, multiplexer bleeding phenomena around bright sources, and other
artifacts. The number of detected sources varied depending on the filter band:
with about 109,000 sources being cataloged in the near-IR bands at 2 - 5
{\mu}m, about 20,000 sources in the shorter parts of the mid-IR bands between 7
- 11 {\mu}m, and about 16,000 sources in the longer parts of the mid-IR bands,
with \sim 4,000 sources at 24 {\mu}m. The estimated 5? detection limits are
approximately 21 magnitude (mag) in the 2 - 5 {\mu}m bands, 19.5 - 19 mag in
the 7 - 11 {\mu}m, and 18.8 - 18.5 mag in the 15 - 24 {\mu}m bands in the AB
magnitude scale. The completenesses for those bands were evaluated as a
function of magnitude: the 50% completeness limits are about 19.8 mag at 3
{\mu}m, 18.6 mag at 9 {\mu}m, and 18 mag at 18 {\mu}m band, respectively. To
construct a reliable source catalog, all of the detected sources were examined
by matching them with those in other wavelength data, including optical and
ground-based near-IR bands. The final band-merged catalog contains about
114,800 sources detected in the IRC filter bands. The properties of the sources
are presented in terms of the distributions in various color-color diagrams.Comment: Accepted for publication in A&A, 23 pages, 27 figure
Diverging UV and Halpha fluxes of star forming galaxies predicted by the IGIMF theory
Although the stellar initial mass function (IMF) has only been directly
determined in star clusters it has been manifoldly applied on galaxy-wide
scales. But taking the clustered nature of star formation into account the
galaxy-wide IMF is constructed by adding all IMFs of all young star clusters
leading to an integrated galactic initial mass function (IGIMF). The IGIMF is
top-light compared to the canonical IMF in star clusters and steepens with
decreasing total star formation rate (SFR). This discrepancy is marginal for
large disk galaxies but becomes significant for SMC-type galaxies and less
massive ones. We here construct IGIMF-based relations between the total FUV and
NUV luminosities of galaxies and the underlying SFR. We make the prediction
that the Halpha luminosity of star forming dwarf galaxies decreases faster with
decreasing SFR than the UV luminosity. This turn-down of the Halpha-UV flux
ratio should be evident below total SFRs of 10^-2 M_sun/yr.Comment: accepted by MNRA
Spatial Clustering of High Redshift Lyman Break Galaxies
We present a physically motivated semi-analytic model to understand the
clustering of high redshift LBGs. We show that the model parameters constrained
by the observed luminosity function, can be used to predict large scale (\theta
> 80 arcsec) bias and angular correlation function of galaxies. These
predictions are shown to reproduce the observations remarkably well. We then
adopt these model parameters to calculate the halo occupation distribution
(HOD) using the conditional mass function. The halo model using this HOD is
shown to provide a reasonably good fit to the observed clustering of LBGs at
both large (\theta>80") and small (\theta < 10") angular scales for z=3-5 and
several limiting magnitudes. However, our models underpredict the clustering
amplitude at intermediate angular scales, where quasi-linear effects are
important. The average mass of halos contributing to the observed clustering is
found to be 6.2 x 10^{11} M_\odot and the characteristic mass of a parent halo
hosting satellite galaxies is 1.2 \times 10^{12} M_\odot for a limiting
absolute magnitude of -20.5 at z=4. For a given threshold luminosity these
masses decrease with increasing z and at any given z these are found to
increase with increasing value of threshold luminosity. We find that
approximately 40 % of the halos above a minimum mass M_{min}, can host
detectable central galaxies and about 5-10 % of these halos are likely to also
host a detectable satellite. The satellites form typically a dynamical
timescale prior to the formation of the parent halo. The small angular scale
clustering is due to central-satellite pairs and is quite sensitive to changes
in the duration of star formation in a halo. The present data favor star
formation in a halo lasting typically for a few dynamical time-scales. Our
models also reproduce different known trends between parameters related to star
formation.Comment: Accepted for publication in MNRA
Photometric redshift accuracy in AKARI Deep Surveys
We investigate the photometric redshift accuracy achievable with the AKARI
infrared data in deep multi-band surveys, such as in the North Ecliptic Pole
field. We demonstrate that the passage of redshifted policyclic aromatic
hydrocarbons and silicate features into the mid-infrared wavelength window
covered by AKARI is a valuable means to recover the redshifts of starburst
galaxies. To this end we have collected a sample of ~60 galaxies drawn from the
GOODS-North Field with spectroscopic redshift 0.5<~z_spec<~1.5 and photometry
from 3.6 to 24 micron, provided by the Spitzer, ISO and AKARI satellites. The
infrared spectra are fitted using synthetic galaxy Spectral Energy
Distributions which account for starburst and active nuclei emission. For ~90%
of the sources in our sample the redshift is recovered with an accuracy
|z_phot-z_spec|/(1+z_spec)<~10%. A similar analysis performed on different sets
of simulated spectra shows that the AKARI infrared data alone can provide
photometric redshifts accurate to |z_phot-z_spec|/(1+z_spec)<~10% (1-sigma) at
z<~2. At higher redshifts the PAH features are shifted outside the wavelength
range covered by AKARI and the photo-z estimates rely on the less prominent 1.6
micron stellar bump; the accuracy achievable in this case on (1+z) is ~10-15%,
provided that the AGN contribution to the infrared emission is subdominant. Our
technique is no more prone to redshift aliasing than optical-uv photo-z, and it
may be possible to reduce this aliasing further with the addition of
submillimetre and/or radio data.Comment: 27 pages, 12 figures, 4 tables. Accepted for publication on MNRA
New abundance measurements in UKS 1927-177, a very metal-poor galaxy in the Local Group
We present new results from optical spectroscopy of the brightest Hii region
in the dwarf irregular galaxy UKS 1927-177 in Sagittarius (SagDIG). From high
signal-to-noise spectra, reddening-corrected line flux ratios have been
measured with typical uncertainties of a few percent, from which the oxygen
abundance is rediscussed, and new abundance estimates are derived for N and Ne.
The O abundance in SagDIG, estimated with the empirical abundance indicator R23
and other methods, is in the range 12+log(O/H)=7.26 to 7.50. The fact that
SagDIG is ~10 times closer than IZw18 makes it an ideal target to test the
hypothesis of the existence of young galaxies in the present-day universe.
Indeed, stellar photometry suggests that this galaxy may harbor a stellar
population older than a few Gyr, and possibly an old stellar component as well.
The case of SagDIG therefore supports the view that very low chemical
abundances can be maintained throughout the life of a dwarf stellar system,
even in the presence of multiple star formation episodes.Comment: 6 pages, 3 figures, accepted for publication in A&A, main journa
Effects of atmospheric stability and urban morphology on daytime intra-urban temperature variability for Glasgow, UK
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